Final: Lecture 22 Flashcards
Musculature of the GI tract:
- Skeletal muscle at either end, including upper esophagus
* Smooth muscle throughout most of the length
Epithelium of the GI tract:
- Stratified squamous at either end for protection and resisting friction
- Simple columnar most of the length
- With glands along most of the length of tract
The GI tract possesses an intrinsic rhythmicity, mostly due to the presence of an _________.
- Enteric nervous system, exists independently of external influences including ANS
- Also receives input from sympathetic and para nervous system
The three peptide neurotransmitters are:
- Bombesin
- Motilin
- Vasoactive intestinal peptide
Unicellular endocrine cells
- Secrete neuropeptides
* Derived from endoderm unlike intrinsic nerve fibers, which are derived from neural crest
Lymphoid tissue
- Most of the immune system is found in the gut*
* MALT (mucosal associated lymphoid tissue) referred to as GALT in the gut tube
GI Protective mechanisms
- Production of large amounts of mucous, assists in lubrication and friction reduction
- Rapid turnover of epithelial cells in harsh environment such as stomach and small intestine (if breaks down you get ulcers)
3 embryonic tissues interact in the development of teeth:
- Ectoderm forms the enamel organ: consists of cells committed to formation of enamel, formed from ectoderm under influence of mesoderm and neural crest
- Neural crest and meso give rise to dental papilla: forms dentin, cementum, and pulp as well as surrounding CT and periodontal pulp
Dentin
- Similar to bone but harder
- 20% of matrix organic (compared to 35% in bone) and composed mostly of collagen type I (second hardest substance in body)
- Synthesized by odontoblasts: line pulp cavity as a single layer of cells, apical processes occupy dentinal tubes
Cementum
- Similar to bone
* Covers dentin of the roots of the tooth
Enamel
- Covers crown of tooth (>97% inorganic)
- Hardest substance in body
- Synthesized by ameloblasts: secreting apical domains = Tomes’ processes
- Specific organic components, rather than collagen, are unique to enamel and are removed after calcification: amelogenins, enamelins
Periodontal ligament
- Highly metabolically active tissue
- Binds cementum to bony socket
- Allows limited movement
- Absorbs pressures of mastication and prevents this pressure from damaging alveolar bone
- Affected by diseases such as diabetes and scurvy
Tongue
- Mass of skeletal muscle covered by stratified suqamous epithelium and elevated projections called papillae
- Filiform papillae: lack taste buds
- Fungiform papillae
- Foliate papillae: rudimentary in adult humans
- Circumvallate papillae
Taste buds
- Contain two types of cells derived from a single stem cell
- Sustentacular cells: support cells
- Taste cells: possess apical microvilli with taste receptors, basal part of cell releases neurotransmitters
Von Ebner’s glands
•Serous glands whose ducts empty into the moats at the bases of the circumvallate papillae